1. Field of the Invention
The invention relates to zoom lens systems for compact video cameras, electronic still cameras, digital cameras, etc. and more particularly to such a high zoom ratio wide-angle zoom lens system having a first lens group of positive diopter, a second lens group of negative diopter, a third lens group of positive diopter, and a fourth lens group of positive diopter so as to have a wide angle of view greater than 70 degrees and more than 10× zoom ratio.
2. Description of Related Art
Recently, compact zoom lens systems as the most important component for a compact video camera, an electronic still camera, digital camera, etc. are developed and commercially available. A compact zoom lens has the benefits of decreasing weight and greatly reducing cost. As a result, for example, the size, weight, and unit price of a compact video camera are decreased greatly.
To achieve the above objective, the focus mechanism is moved from the front element (or first element) to the least lens set. It has the benefits of greatly reducing the size of the first lens group so as to achieve the goal of minimizing the zoom lens system. This in turn can decrease power required for focusing. Therefore, a quick focusing can be achieved.
However, aberration of the rear focusing arrangement is not easy to control. This in turn can increase the difficulty of focusing and lower the image quality due to the increase of zooming range.
Moreover, there are a number of drawbacks associated with rear focusing arrangement systems such as lower resolution, limited angle of view (or angle in short), great distortion, somewhat bulky for carry, and inconvenience in use.
For a digital video camera (DVC) having the features of being lightweight and compact, its lens system cannot achieve the goal of having a wide angle (e.g., about 60-degree of angle) due to optical limitations. Further, there is no suggestion in prior art literatures about a high zoom ratio wide-angle zoom lens system having at least 64-degree angle. Thus, the need for improvement still exists.